Lighting used for general purposes should preferably be white. Energy-efficient lighting can be obtained by making use of light-emitting diodes (LEDs). LEDs emit light with a very narrow wavelength-band, thereby producing strongly colored light. To obtain white light as required for general purpose lighting 2 main techniques are used. Either light from red, green and blue LEDs is combined or a blue light emitting diode is used in combination with certain phosphors that absorb a part of the blue light and emit light with a broader spectrum of white light.
WO2006/135840 describes a thermally conductive polyamide-based composition that can be used in the manufacturing of components that are used in light-emitting diodes. The composition comprises a semi-aromatic polyamide and at least 30 weight percent of a thermally conductive material.
However, a disadvantage of a composition as described in WO2006/135840 is not only that the addition of a thermally conductive material raises the cost price of the composition and thus of the parts that are made out of that composition, but more importantly, the addition of the thermally conductive material negatively influences the properties of the composition and deteriorates its processing behavior.
Under the influence of blue light and the increased temperature, that inevitably results from the fact that a light source always produces heat next to light, the material that is used to produce components for light-emitting diodes tends to show discoloration. The surface of the material starts to display brown areas. This is sometimes also called yellowing. This yellowing is not only from an aesthetical point of view undesirable. It also diminishes the light yield that is coming from the LED, which is very undesirable, especially in view of environmental concerns.
Although the composition in WO2006/135840 can be used in the manufacture of components that are used in light-emitting diodes, the components suffer from an unsatisfactory performance on certain ageing tests. Therefore there is a need for an improved composition that can be used in the production of components for light-emitting diodes, that is cost effective and that displays improved results for certain ageing behavior, especially an improved resistance against yellowing.
This object is reached by a polymer composition comprising:
                a. 90 to 40 wt % of one or more semi-aromatic polyamides and        b. 10 to 60 wt % of one or more of aliphatic polyamides and        c.1 at least one white pigment as secondary component and        c.2 optionally one or more other secondary components,        wherein the sum of the amount of semi-aromatic and aliphatic polyamide is 100 wt % and wherein:                    the semi-aromatic polyamide is derived from one or more aliphatic diamine monomers containing 4 to 12 carbon atoms and one or more benzene dicarboxylic acid monomers and            the aliphatic polyamide is derived from one or more aliphatic diamine monomers containing 4 to 10 carbon atoms and one or more aliphatic dicarboxylic acids with 6 to 12 carbon atoms                        with the proviso that no additional thermally conductive material is present in the composition.        